io6 



CYTOLOGY 



CHAP. 



The last case is perhaps the most remarkable, the X group consisting 

 of two large and three very small constituents (Figs. 49, 50). 



The chromosome equipment of the various examples is as follows 

 (omitting Protenor and Lygaeus, which have already been dealt with) : 

 n' stands for the haploid number of ordinary chromosomes, and the 



AnaphaseJL 

 in (S. 



Two classes of 

 spermatozoa.. 



Reduced number Male artdfemaJLe 

 of chromosomes chromosome 



in the egq. groups. 



oOq 



° ••• 



o •• O 



oOo 



+ 



o •• - 











o 









§l^o^8 



0*0 930 





a 



}fo'o°6 



26 



Fig. 50. 



Diagram of the results of fertilization in Acholla multispinosa. (Payne, BM., 1910.) 

 The sex chromosomes shown in black. 



number of components of the X chromosome is represented by the 

 suffixed numeral. 



Male. 

 Diploid Group. Gametes, 



w' + X, 

 Syromastes (Wilson, 1909 a), m'=io 2h' + Xo 



Female. 

 Diploid Group. Gametes. 



Ascaris lumhricoides (Edwards, ^ 

 1910), w'=i9 / 



Fitchia (Payne, 1909), n'=i2 

 Prionidus (Payne, 1 909) , n' = 1 1 

 Gelastocoris (Payne, 1909), n'=i^ 

 Acholla (Payne, 1909), n'=io 



2n' + X, 

 an' + X.Y 



2«' + X3Y 



2m' + XiY 

 2«' + X,Y 



n 



m' + Xj 



«' 



m' + X., 



«' + Y" 



m' + X3 



n' + Y 

 n' + X^ 

 n' + Y 

 «' + X, 

 n' + Y 



2n' + X.,X, 

 2n' + X,X, 



ZM' + X^X^ 



2M' + X3X3 



2n' + X^X^ 



2>t' + XjX, 



M' + X, 



«' + x, 



n' + X, 

 n' + X3 

 «' + X^ 

 m' + X. 



Thus in Acholla the female group has four more chromosomes than 

 the male, the actual numbers being 30 and 26. 



(4) Behaviour of the Sex Chromosomes during Syndesis and the Meiotic 

 Prophase, and outside the Meiotic Phase 



As was illustrated in the case of Lygaeus, the sex chromosomes in 

 the male retain a compact form, while the other chromosomes are in 



